A radar apparatus that receives a reflected wave signal having been reflected on a target with an array antenna and measures a phase difference between signals received by respective receiver antennas so as to estimate an arrival direction with resolution higher than the main beam width of the receiver array antenna is known.
As a known method for estimating an arrival direction based on a phase difference between received signals received by an array antenna in a conventional radar apparatus, for example, the Fourier technique, the Capon method and the like are known. In employing the Fourier technique, the radar apparatus calculates a correlation matrix of received signals received by respective receiver antennas, and estimates, as the arrival direction, an azimuth at which an evaluation function using the correlation matrix gives a peak value. Alternatively, in employing the Capon method, the radar apparatus calculates an inverse matrix of a correlation matrix of received signals received by respective receiver antennas, and estimates, as the arrival direction, an azimuth at which an evaluation function using the inverse matrix of the correlation matrix gives a peak value.
As a related art for estimating an arrival direction of radio waves by using a correlation matrix obtained from received signals received by an array antenna, for example, Patent Document 1 is known. A radio wave arrival direction estimating device disclosed in Patent Document 1 specifies a beat frequency at which a frequency spectrum of a beat signal obtained by each of a plurality of receiver antennas has a peak value, and extracts not only a frequency spectrum of the specified beat frequency at which the peak value is attained but also a prescribed number of frequencies (target frequencies) belonging to the same peak waveform.
The radio wave arrival direction estimating device generates individual correlation matrixes by using reception vectors obtained by arranging sampling data of the same target frequency sampled from FFT results of all received channels, and the individual correlation matrixes are further subjected to weighted addition and averaging to generate an average correlation matrix. The radio wave arrival direction estimating device obtains an arrival direction of reflected waves received by the respective receiver antennas, namely, a direction where a target to be detected is present, by MUSIC (Multiple Signal Classification) method using the average correlation matrix.
In this manner, the radio wave arrival direction estimating device can secure, in a short time, the number of snapshots necessary for generating an average correlation matrix in which correlation between incoming waves is sufficiently suppressed without increasing the number of antennas and receivers, and hence, the accuracy in estimating a radio wave arrival direction can be improved without increasing the device scale or production cost.